(1) Field of the Invention
The present invention relates to an optical module having an optical element, such as a laser-diode or a photo-diode, connected to an optical fiber, and to a method of producing the optical module. More particularly, the present invention relates to an optical module in which the optical element is supported on a mounting board and connected to an optical fiber.
Recently, optical fiber transmission has made great progress. The optical fiber transmission has various advantages including transmission of a large amount of data, a low level of loss, no cross talk, no radiation and the like. In order to develop an optical fiber transmission system for practical use, it is important that optical parts, like the optical module, which constitute a part of the optical fiber transmission system, have high reliability and good productivity.
(2) Description of the Related Art
FIGS. 1A, 1B and 1C show a conventional optical module. Referring to FIGS. 1A, 1B and 1C, an insulating layer 7 is formed on a mounting board 1.
The mounting board 1 is comprised of a silicon (Si) substrate, and the insulating layer 7 is a silicon dioxide (SiO.sub.2) film. A metal layer 2 is formed on the insulating layer 7 as shown in FIG. 1A. A V-groove 4 is formed in the middle of the mounting board 1, the V-groove 4 extending in a longitudinal direction of the mounting board 1. An optical fiber 8 is enclosed by the V-groove 4. The V-groove 4 extends in a direction of the optical axis of the optical fiber 8.
FIG. 1B is an enlarged view of a portion of the conventional optical module where a laser-diode (LD) 3 and the optical fiber 8 are connected. As shown in FIG. 1B, a solder layer 9 is formed adjacent to an end of the V-groove 4, and the solder layer 9 is used to fix the laser-diode (LD) 3 to the mounting board 1. An electrode 5 is formed on the insulating layer 7. The electrode 5 is made of gold (Au). The electrode 5 is connected to and taken out from the solder layer 9, and the electrode 5 extends from the end of the solder layer 9 in the longitudinal direction of the mounting board 1.
The laser-diode (LD) 3 is positioned at a packaging location 10 on the mounting board 1 to correctly perform the coupling of the laser-diode 3 and the optical fiber 8 with respect to the direction of the optical axis of the optical fiber 8. The packaging location 10 is indicated by a dotted line in FIG. 1B, and it surrounds the periphery of the solder layer 9. A positioning mark 11 is provided on the mounting board 1 and attached to the electrode 5, and the positioning mark 11 is used to indicate the packaging location 10 for positioning the laser-diode 3 on the mounting board 1 at a proper location. The positioning mark 11 has a rectangular shape, and it is located at an opposite side to a side of the packaging location where the V-groove 4 is formed.
FIG. 1C is a cross-sectional view of the portion of the conventional optical module shown in FIG. 1B. As shown in FIG. 1C, the V-groove 4 has a sloping wall 4a which confronts the leading edge of the optical fiber 8. Since the sloping wall 4a of the V-groove 4 comes in contact with the optical fiber 30 when the optical fiber 8 is placed in the V-groove 4 to approach the laser-diode 3, the conventional optical module requires a certain amount of gap 12 between the laser-diode (LD) 3 and the optical fiber 8. To reduce the gap 12 between the LD 3 and the optical fiber 8, it is necessary that the packaging position of the LD 3 on the mounting board 1 is a position at which the LD 3 projects from the end of the V-groove 4 toward the V-groove 4, as shown in FIG. 1C.
If the positioning mark 11 is located adjacent to the V-groove 4, the positioning mark 11 is concealed by the LD 3 and it cannot be used to position the LD 3 on the mounting board 1 during the assembly.
The V-groove 4 is formed by etching of the silicon board 1, and the V-groove 4 has to include a sloping surface. This sloping surface depends on the characteristics of the silicon crystal structure of the silicon board 1. The sloping surface of the V-groove 4 confronts the leading edge of the optical fiber 8 when inserted.
The above conventional optical module, shown in 1A, 1B and 1C, has a problem, that is, it is difficult to perform the positioning of the laser-diode 3 to the optical fiber 8 with high accuracy. To perform the positioning of the laser-diode 3, one must observe the positioning mark 11 which is located at the opposite side to the side of the packaging location 10 where the V-groove 4 is formed. In particular, it is very difficult to achieve a required level of accuracy of the positioning of the laser-diode 3 by eliminating a misalignment or rotation of the laser-diode 3 with respect to the direction of the optical axis of the optical fiber 8. Since the positioning of the optical element on the mounting board is difficult to perform, the conventional optical module produced by using the above production method is not reliable, and the productivity of the thus produced optical module is low.